I pulled my 22A out of the vault today and the rubber grip inserts felt very sticky, so I called S&W to check it out. The Rep I talked to said that is very common and no cause for alarm. I hit it with some silicon spray and a thorough wipe down and they felt normal again. Many thanks to Smith & Wesson.
Panda
They hold a lot of moisture under the grips too. The guns I have them on I take them off often to wipe everything down with CLP.
Similar to the trip material on my Gerber Gator I bet. Mine's 30 years old and beginning to actually flake away. I'm considering maybe sending it back to Gerber to test their lifetime warranty. 
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